8325870: Zap end padding bits for ArrayOops in non-release builds

[xmas92]

Make ObjArrayAllocator zap the end padding bits in not PRODUCT builds.

Issues like JDK-8325074 / #17863 would then reproduce deterministically. Avoid future regressions.

Guarded Copy::fill_to_bytes, it was not clear if or how it handles count == 0. Given that almost all dispatch to memset, the count == 0 would probably be alright, but as obj_end - padding_in_bytes may point beyond an object and thus outside the heap it seems prudent to guard it (I believe memset requires a valid pointer).

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Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
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• Commit message must refer to an issue

Issue

• JDK-8325870: Zap end padding bits for ArrayOops in non-release builds (Enhancement - P4)

Reviewers

• Stefan Karlsson (@stefank - Reviewer)
• Albert Mingkun Yang (@albertnetymk - Reviewer)

Reviewing

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• 01: Full - Incremental (eec91e9e)
• 00: Full (9504304e)

[openjdk]

@xmas92 This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8325870: Zap end padding bits for ArrayOops in non-release builds

Reviewed-by: stefank, ayang

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 72 new commits pushed to the master branch:

• 0f4cd8f: 8326414: Serial: Inline SerialHeap::create_rem_set
• 8b30503: 8323695: RenderPerf (2D) enhancements (23.12)
• 8e5f6dd: 8324243: Compilation failures in java.desktop module with gcc 14
• 0bcece9: 8325342: Remove unneeded exceptions in compare.sh
• 64f7972: 8326158: Javadoc for java.time.DayOfWeek#minus(long)
• f0f4d63: 8326351: Update the Zlib version in open/src/java.base/share/legal/zlib.md to 1.3.1
• 51e2dde: 8326235: RISC-V: Size CodeCache for short calls encoding
• c022431: 8326412: debuginfo files should not have executable bit set
• 33834b7: 8326375: [REDO] Clean up NativeCompilation.gmk and its newly created parts
• 2352268: 8326334: JFR failed assert(used(klass)) failed: invariant
• ... and 62 more: https://git.openjdk.org/jdk/compare/4018b2b19629ddb8cd7a56e064dfef371f23e5fa...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[albertnetymk]

/label add hotspot-gc

[openjdk]

@albertnetymk
The hotspot-gc label was successfully added.

[xmas92]

Thanks for the reviews.
/integrate

[openjdk]

Going to push as commit 10eafdc.
Since your change was applied there have been 72 commits pushed to the master branch:

• 0f4cd8f: 8326414: Serial: Inline SerialHeap::create_rem_set
• 8b30503: 8323695: RenderPerf (2D) enhancements (23.12)
• 8e5f6dd: 8324243: Compilation failures in java.desktop module with gcc 14
• 0bcece9: 8325342: Remove unneeded exceptions in compare.sh
• 64f7972: 8326158: Javadoc for java.time.DayOfWeek#minus(long)
• f0f4d63: 8326351: Update the Zlib version in open/src/java.base/share/legal/zlib.md to 1.3.1
• 51e2dde: 8326235: RISC-V: Size CodeCache for short calls encoding
• c022431: 8326412: debuginfo files should not have executable bit set
• 33834b7: 8326375: [REDO] Clean up NativeCompilation.gmk and its newly created parts
• 2352268: 8326334: JFR failed assert(used(klass)) failed: invariant
• ... and 62 more: https://git.openjdk.org/jdk/compare/4018b2b19629ddb8cd7a56e064dfef371f23e5fa...master

Your commit was automatically rebased without conflicts.

[openjdk]

@xmas92 Pushed as commit 10eafdc.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.